Field of the Invention
The present invention relates to a fluid processing tube or storage container and a method for analyzing a fluid. More specifically, the present invention relates to a tube and a method for in-line quantification of including but not limited to DNA, RNA, salts and proteins by optical analysis techniques. In particular, the present invention relates to quantification of including but not limited to DNA, RNA, safe and proteins by measuring optical transmittance.
Description of Related Art
In many technical fields like chemistry, biology, medicine or environmental protection, fluids have to be analysed before, during or after being stored, processed or brought into reaction with each other. For this purpose, fluids are centrifuged, stored, mixed, filtered, cooled, heated, decomposed, washed, pipetted, or treated by other procedures. In order to prepare and analyze a fluid, often a long sequence of analyzing and processing steps, which may be iterative, is necessary. In many cases, large sets of different fluids need to be processed and analyzed according to the same procedure. Sometimes, sequences or batches of the same fluid need to be processed and analyzed in parallel.
Optical analysis procedures are known in the art and frequently used to analyze fluids. Optical analysis may include measuring transmittance, fluorescence, chemoluminescence, bioluminescence and fluorescence resonance energy transfer (FRET). In many cases, a fluid is optically analyzed by measuring optical transmittance. Transmittance is the fraction of incident light of a beam at a specified wavelength that passes through a sample. The term “light” according to the present invention refers to electromagnetic radiation of any wavelength, in particular, the term light refers to electromagnetic radiation in the wavelengths of ultraviolet and visible light. Most preferably, the term light refers to electromagnetic radiation in the wavelengths of about 220 to about 400 nm (ultraviolet light). By measuring the intensity of the light coming out of the sample, absorbance and optical density of a fluid at a certain wavelength or many different wave-lengths can be assessed.
In a fluid, according to Beer-Lambert's law, absorption is linearly dependent on the length of the optical path, the molar extinction coefficient of the absorbing chemical species and the concentration of the chemical species in the fluid. The length of the optical path is the distance that the lightbeam travels in the fluid. Thus, for example, when the length of the optical path and the molar extinction coefficient of a chemical species are known, the concentration of the species in the fluid can be assessed. For quantifying salts, DNA, RNA and proteins and assessing their concentrations within a fluid, it is desirable to measure optical transmittance at the wavelengths of about 230 nm (salts), of about 280 nm (DNA and RNA) and of about 280 nm (proteins). In order to quantify all compounds in a single measurement, it is particularly desirable to measure optical transmittance over the entire range of about 220 to about 400 nm.
Generally, a container for containing a fluid is used in optical analysis. The side-wall of such a container comprises at least one area which does not absorb, refract or reflect light in the wavelengths of interest for the optical analysis procedure or only absorbs, refracts or reflects a small fraction thereof. Cyclic olefin copolymers, cyclic olefin polymers, polymethylpenten, graphene and PTFE are known for showing no or low absorption of light for a wide range of wavelengths.
Apparatuses for measuring transmittance, for example spectrophotometers, generally allow assessing absorption exactly in a specified range of absorptions. As absorption is linearly dependent on the length of the optical path and the concentration of the chemical species, measuring absorption for optical paths of different lengths is frequently desirable, in order to assess a wide range of concentrations of different chemical species. To minimize the lightbeam from being refracted or reflected, the side-wall of the container containing the fluid should be perpendicular to the lightbeam at the points where the beam passes through the side-wall.
Small volumes of fluids are often processed and stored in microcentrifuge tubes commonly known as Eppendorf tubes. Microcentrifuge tubes are small, cylindrical plastic containers, typically having conical bottoms and a closable cap. They are frequently made from polypropylene and considered to be disposable.
However, commonly used microcentrifuge tubes are not suitable for optical analysis, because they are not transparent enough in the desired wavelengths. Reasons for this may be, inter alia, the polymers used being crystalline or partly crystalline, the polymeric materials absorbing light in the same wavelengths as the chemical species or the configuration of the tube side-wall leading to reflection and/or refraction of the light beam. In particular, the material used for microcentrifuge tubes absorbs light in the wavelengths of 220 to 240 nm and is partly crystalline. Thus, microcentrifuge tubes do not allow quantification of DNA, RNA, salts and proteins. Furthermore, microcentrifuge tubes do not provide optical paths of different, predefined lengths.
Thus, fluids processed in commonly used microcentrifuge tubes have to be transferred to other containers for being optically analyzed. Therefore, the microcentrifuge tube has to be opened and the fluid transferred, e.g., pipetted. This may be time consuming, limit the throughput and be prone to errors during the procedure. In particular, when a long sequence of analyzing and processing steps is necessary to prepare and analyze the fluid, large sets of different fluids need to be processed and analyzed according to the same procedure, or sequences or batches of the same fluid need to be processed and analyzed in parallel. Opening or transferring the sample also involves the risk of contamination. Furthermore, opening or transferring the sample involves the risk of sample loss, e.g. by evaporation or because crops remain in the tube or the pipette. When the fluid has to be transferred several times, because the optical path of the container selected is to short or to long, risks of contamination and sample loss are even greater. Having to open the tube and transferring the content also requires additional steps in automated in-line processing and analysis apparatuses.
Furthermore, commonly used microcentrifuge tubes are not suitable for carrying out certain processing, storing, and reaction steps, in particular, commonly used microcentrifuge tubes are not resistant to some regularly used solvents, which may also be used for optical analysis.
Containers for optical analysis can not be used for storing and processing fluids. For example, they can not be suitably closed. One reason for this is that the materials used for the containers are not soft enough to allow configuration of a closable cap. In particular, no containers having a cap attached over a joint to the fluid containing part of the container are known in the art. However, when the cap is not attached to the fluid containing part of the container, this may lead to errors during the procedure and cross contamination, e.g., when caps are accidentally interchanged. Furthermore, loose caps may pose problems for automated in-line processing apparatuses, e.g., because the caps will fall off when opened.